Mural thrombi probably develop on the left ventricular (LV) endocardial surface of all patients with transmural LV myocardial infarction (MI). The thrombi are nearly always attached over a broad surface and protrusion into the left ventricular cavity is limited. They may be demonstrable by echocardiography. We recently studied a 54-year-old man who died 6 months after an acute MI and had a most unusual LV thrombus. Two-dimensional echocardiogram post-operatively disclosed a "free floating" mass in the LV cavity. At necropsy, an 11-cm long LV pedunculated thrombus attached by a stalk less than 1 cm broad to the endocardium over a healed transmural MI was present.